1. Field of the Invention
The present invention relates to a method for producing ytterbium phosphate fine particles.
2. Description of the Related Art
Ytterbium phosphate (YbPO4) absorbs light in the infrared region but does not absorb light in the visible light region (Japanese Patent Laid-Open No. 08-209110). Ytterbium phosphate has a certain refractive index in the visible light region. For example, refractive indices (nod and ned) and Abbe numbers (vod and ved) of ytterbium phosphate in terms of ordinary ray and extraordinary ray with the d line (λ=587.6 nm) are as follows.nod=1.676,ned=1.853vod=66,ved=78
These optical constants show that ytterbium phosphate has high refractive indices and high Abbe numbers. That is, ytterbium phosphate does not absorb light in the visible light region and can be used as a high-refractive-index low-dispersion material.
Accordingly, an organic-inorganic composite material including nanoparticles of ytterbium phosphate can be used for forming a colorless transparent optical lens having a high refractive index and a low dispersion. Such nanoparticles of ytterbium phosphate can be made to have a crystallite size of 10 nm or less. When an inorganic material having a crystallite size of more than 10 nm is used, light scattering is increased due to the difference in refractive index between the inorganic material and an organic material and haze may be increased.
A sol-gel process employing an ytterbium alkoxide as a raw material has been used as a method for producing ytterbium phosphate (YbPO4) fine particles (Japanese Patent Laid-Open No. 08-209110).
A nonaqueous reaction is also known in which an ytterbium trichloride hydrate is used as a raw material, water is removed from the hydrate in an ether solvent, and the resultant ytterbium trichloride reacts with phosphoric acid (O. Lehmann et al., J. Phys. Chem. B, vol. 107, p7449 to 7453 (2003)).